According to American Diabetic Association's position statement, the glycemic index measures blood glucose rise after the ingestion of a constant amount of a carbohydrate-containing food. The index is calculated in reference to a food with high glycemic index, e.g. glucose or white bread. Developed by Dr. David Jenkins in 1981, the glycemic index remains a popular tool for making healthy food choices. However, the index has limitations and should not be used as the only index for diet planning.
Myth: Glycemic Index of a Food Does Not Change
Glycemic index of the same food can vary depending on the conditions and preparations. Ripeness, acidity, cooking method and time, the presence of fiber, fat, and protein, and the degree of processing can all influence the glycemic index of a food. For example, juice prepared from an orange will have a higher glycemic index than a whole orange because juice is more processed and refined, even though they are essentially the same food.
Myth: Foods from the Same Family Share One Glycemic Index
Foods from the same family can have quite different glycemic indexes. For example, long-grain rice has a lower glycemic index than short-grain sticky rice. Even foods grown in different places can have different glycemic indexes. Australian potatoes have glycemic indexes of 87 to 101, whereas Canadian potatoes have much lower glycemic indexes at 59 to 70.
Myth: Low Glycemic Index Diet Lowers Blood Glucose
Although a low glycemic index diet may acutely lower the post-meal glucose response when compared with a high glycemic index diet, whether it lowers blood glucose in general is still controversial. A review of 14 studies published in Diabetic Care in 2003 concluded that a low glycemic index diet produced a small 0.4 percent decrease in hemoglobin A1C, a common measure of blood glucose control in diabetics. However, such a decrease was only seen in comparison with high glycemic index diet. As most people already consume a medium glycemic index diet, it's not known if pushing the glycemic index lower will decrease the blood glucose in the general population.
Myth: Glycemic Index Can Be Used in Place of Common Diabetic Management Tools
The American Diabetic Association recommends that diabetic patients continue to use carbohydrate counting and the exchange system for meal planning and carbohydrate estimation. The glycemic index can be used as an adjunct, but should not replace these standard diet planning tools for diabetics.
Myth: Low Glycemic Index Diet Causes Weight Loss
Studies on low glycemic index diets and weight loss produced mixed results. This is likely due to the individual differences in response to carbohydrate-containing foods, as well as the variability in total carbohydrate intakes, which were not always accounted for by the studies. Low glycemic index foods are useful for weight-loss because they suppress appetite, but no conclusive evidences suggest that employing them will lead to weight loss.
Glycemic Index is Always a Good Indicator of Healthy Food Choices
Foods high in fats and proteins are generally low in glycemic index yet are not necessarily healthy. For example, ice cream and red meats have low glycemic indexes but they are also high in saturated fat. Snickers bars have a low glycemic index of 55, similar to that of a banana. Yet, banana is a better food choice because it has more fibers, vitamins and minerals with fewer calories.
References
- American Diabetic Association: Nutrition Recommendations and Interventions for Diabetics
- American Journal of Clinical Nutrition: International table of glycemic index and glycemic load value; Kaye Foster-Powell et al.; 2002
- Diabetic Care: Low-glycemic Index Diets in the Management of Diabetes: a Meta-analysis of Randomized Controlled Trials; Brand-Miller J et al.; 2003
